That’s the beauty of UBI! No one has to be generous. It’s paid through taxes so everyone pays based on their means and ability.

He clearly doesn't expect everyone to be generous, hence why he advocates for UBI. UBI would be mandated and would therefore force participation from those without such generosity (according to their means, of course). By claiming that he holds a viewpoint which he obviously does not you've utterly failed to refute his argument. Perhaps you should seriously consider why his argument works and yours doesn't. You may come to a surprising change in your point of view.